Sheet Feeders

ABSTRACT

A sheet feeder comprises a feed deck for supporting a stack of sheets ( 65 ) to be fed. The feed deck may be formed by a bed of freely spinning rollers. A feed block ( 62 ) comprises a friction pad ( 66 ) that projects from the bottom of the feed block ( 62 ) towards a drive belt ( 42 ) to define a gate therebetween. The drive belt ( 42 ) frictionally engages the underside of a bottom sheet of the stack ( 65 ) and urges the sheet towards the gate. The feed block ( 62 ) comprises a front face ( 72 ) immediately upstream from the gate, which is inclined at a sharp angle to the feed direction. The friction pad ( 66 ) comprises a lower face that is substantially parallel to the feed direction and does not intersect the plane of the feed block front face ( 72 ).

FIELD OF THE INVENTION

The invention relates to sheet feeder apparatus, which separates sheetsof paper or card from a stack and feeds them individually from theapparatus in a direction parallel to the plane of the sheets. The sheetfeeder may be part of a device for processing the paper, for example bycreasing, perforating or cutting it between a pair of rollers or it maysimply deliver the individual sheets to a separate device for furtherprocessing. The nature of the downstream operation does not form part ofthe present invention.

The sheets handled by the feeder may comprise paper or cardboard, forexample in the density range 50 gm² to 500 gm², or other similarmaterials such as thin plastics. For simplicity, and without limitation,the material will be referred to hereafter as “paper”.

BACKGROUND OF THE INVENTION

Sheet feeders are known that use a drive means such as a belt or rollerto remove a single sheet laterally from the bottom of a stack of sheetsthat rests on a feed deck. The bottom sheet resists separation from thestack owing to friction with the next sheet in the stack above it andwith the non-moving parts of the feed deck below it. In order for thesheet to slide away from the stack, the grip between the sheet and thedrive means must exceed those frictional forces. Ideally, that should betrue whether the bottom sheet is weighed on by a full stack or by only afew sheets.

Friction between the moving sheet and the stationary parts of the feeddeck has a tendency to cause scuff marks on the surface of the paper.That is a particular problem with the increasing use of digital printingon paper with a smooth surface.

Some sheet feeders have used suction drums to improve the grip betweenthe drive means and the paper. The surface of a suction drum isperforated by holes and an air pump is provided to suck air from theinterior of the drum so that the paper clings to the drum's surface. Theair pump may also be used to direct a jet of air towards the edge of thestack in order to assist with separating the sheets of the stack.However, such air pumps add to the bulk and complexity of the sheetfeeder as well as its running costs and noise levels.

A sheet feeder should be able to deliver the sheets as fast as possible,up to the maximum operating speed of any downstream processingapparatus. It should reliably deliver only a single sheet at a timebecause a misfeed in which two sheets are delivered together will atbest not be processed properly downstream and may at worst jam theapparatus, causing a costly delay in workflow.

SUMMARY OF THE INVENTION

In a first aspect, the invention provides a sheet feeder comprising: afeed deck for supporting a stack of sheets to be fed; a feed block; adrive belt for frictionally engaging the underside of a bottom sheet ofthe stack and urging the sheet along a feed direction below the feedblock; the feed block comprising a friction pad that projects from thebottom of the feed block towards the drive belt to define a gatetherebetween and a first front face immediately upstream from the gate,the first front face defining a plane inclined at a first angle to thefeed direction, wherein the friction pad does not intersect the plane ofthe first front face.

A sheet feeder made in accordance with the invention is found to feedsingle sheets rapidly and reliably over a wide range of paperthicknesses and a wide range of stack heights. It runs quietly becauseit does not rely on air pumps and it reduces scuffing of the surface ofthe sheets.

The first angle may be less than 45° and is preferably between 25° and30°.

The feed block may further comprises a second front face upstream fromthe first front face, the second front face being inclined to the feeddirection at a second angle that is greater than the first angle.

The feed block may further comprise a lower face, which is locateddownstream from the first front face and which faces the drive belt, thefriction pad projecting from the bottom of the feed block below thelower face. Preferably the lower face of the feed block defines a planethat is substantially parallel to the feed direction; the feed blockfurther comprising a curved surface that effects a smooth transitionfrom the first front face to the lower face. A suitable material for thefeed block is aluminium or an aluminium alloy; and at least the firstfront face of the feed block may be anodized.

The friction pad preferably comprises a pad lower face that issubstantially parallel to the feed direction. It may further comprises apad front face that adjoins an upstream end of the pad lower face, thepad front face being inclined at an angle of less than 45° to the feeddirection where it adjoins the pad lower face.

In a preferred sheet feeder according to the invention, a pair of thedrive belts are positioned on opposite sides of a centreline of thefeeder and pair of the feed blocks are aligned with respective ones ofthe drive belts.

The pair of feed blocks may be mounted on a common bracket, which is inturn mounted on a frame of the sheet feeder. Means may be provided foradjusting the height of at least one of the feed blocks relative to thebracket or for adjusting the height of the bracket relative to theframe.

In a second aspect, the invention provides a sheet feeder comprising: afeed deck for supporting a stack of sheets to be fed; a feed block; anddrive means for frictionally engaging the underside of a bottom sheet ofthe stack and urging the sheet along a feed direction at a first speedthrough a gate defined between the feed block and the drive means; thesheet feeder further comprising a counter-rotating pair of accelerationrollers downstream from the gate for gripping a sheet between them andurging the sheet away from the gate at a second speed higher than thefirst speed. The second speed may be at least twice the first speed andis preferably about five times the first speed.

The increase in the speed at which the sheets are transported causesgaps to open up between successive sheets, which can improve theirhandling downstream of the sheet feeder.

In a third aspect, the invention provides a sheet feeder comprising: afeed deck for supporting a stack of sheets to be fed; a feed block; anddrive means for frictionally engaging the underside of a bottom sheet ofthe stack and urging the sheet along a feed direction through a gatedefined between the feed block and the drive means; wherein the feeddeck is inclined to the horizontal and wherein the feed deck comprises aplurality of feed rollers, each of which is free to spin about agenerally horizontal axis.

By allowing the moving sheets to travel on freely spinning rollers inthe areas where they are not in contact with the guide means, thereliability of feeding the sheets is improved and scuffing of theirsurface is reduced.

The sheet feeder may further comprise at least one guide plate arrangedin a vertical plane and transversely to a series of the rollers, theseries of rollers defining a plane of the feed deck that is tangent tothe tops of the rollers; wherein a lower edge of the guide plateprojects below the plane between adjacent pairs of the rollers.

In a fourth aspect, the invention provides a sheet feeder comprising: afeed deck for supporting a stack of sheets to be fed; a feed block; anddrive means for frictionally engaging the underside of a bottom sheet ofthe stack and urging the sheet along a feed direction through a gatedefined between the feed block and the drive means; wherein the drivemeans is part of a removably mounted unit in the feed deck. This permitsworn parts of the drive means, such as belts or rollers, to be replacedeasily and in a short time.

Preferably, the drive means unit comprises means at one end of the unitfor pivotally mounting the unit in the feed deck; and means at the otherend of the unit for fastening the unit to the feed deck. The pivotalmounting means may comprise jaws on the drive unit for engaging a rod onthe feed deck, or vice versa. The drive unit may also comprise a firstgear for engaging a second gear below the feed deck, from which powerfor the drive means is derived.

DRAWINGS

FIG. 1 is a side elevation of a paper creasing machine, which includes asheet feeder in accordance with the invention.

FIG. 2 is a plan view of part of the machine shown in FIG. 1.

FIGS. 3, 4 and 5 are respectively a plan view, a side elevation and afront elevation of the drive unit and feed block of the machine shown inFIG. 1.

FIG. 6 is a schematic elevation of a side guide of the machine shown inFIG. 1.

FIGS. 7, 8 and 9 are respectively a side elevation, a plan view and afront elevation of the feed block and mounting bracket of the machineshown in FIG. 1.

FIGS. 10 and 11 are side elevations of respectively the feed block andthe friction pad of the machine shown in FIG. 1, marked up to showpreferred dimensions.

DETAILED DESCRIPTION

FIG. 1 shows a machine 2 for creasing, perforating or cutting sheets ofpaper from a stack. A stack of paper to be processed (not shown) isplaced on a feed deck 4, supported by side guides 6. A sheet feederdevice in accordance with the present invention separates individualsheets of paper from the bottom of the stack and feeds them into thebody 8 of the machine 2 along the plane of the feed deck 4. After aprocessing operation such as creasing, perforating or cutting by themachine 2, the processed sheets are collected as an output stack in anoutput bin 10. Alternatively, the processed sheets could be deliveredindividually on rollers to other machinery for further operations to becarried out.

A control panel 12 allows an operator to control aspects of theoperation of the machine 2, such as its speed, in a conventional manner.An emergency stop button 14 is provided in a prominent and easilyaccessible location.

FIG. 2 is a plan view of the sheet feeder of the creasing machine 2,also showing the creasing device 20 but not the output bin 10. The feedblock (described below) that defines the gate 26 of the sheet feeder isalso omitted to show details of the drive unit 40. A stack of paper (notshown in FIG. 2) rests on the feed deck 4 overlapping the drive unit 40,which acts on the lowest sheet of the stack to feed the sheet into themachine in the direction marked by an arrow 24. The drive mechanism ofthe sheet feeder will be explained in more detail below but in FIG. 2 itcan be seen that the drive unit 40 comprises a pair of drive belts 42with upper surfaces that lie generally in the plane of the feed deck 4.

The majority of the surface of the feed deck 4 is formed by sets of feedrollers 22. There are sets of feed rollers 22 to each side of the driveunit 40 to support the areas of the paper in the stack that do notoverlie the drive unit. Each of the rollers 22 is mounted so that it canspin freely about its axis, with minimal resistance. The axes of therollers 22 are generally horizontal and are perpendicular to thedirection in which the sheets move. Because the plane of the feed deck 4is inclined from the horizontal, as shown in FIG. 1, a stack of paperplaced on the feed deck 4 will roll down the slope of the deck towardsthe position of the gate 26 of the sheet feeder.

An upstream part of the feed deck 4 may be formed as a removableextension 28, which at the user's option can be present in order toallow larger sheets of paper to be stacked or can be absent in order toreduce the footprint of the machine 2. The removable extension 28comprises further sets of rollers 22. Over the majority of the feed deck4, the surface is thus defined by feed rollers 22. Wherever anysignificant level of friction occurs between a sheet and a roller, thefree-spinning roller can simply rotate to follow the movement of thesheet and thus scuffing of the sheet's surface is substantially avoided.

The sides of the stack on the feed deck 4 are supported by a pair ofside guides 6. The side guides 6 are generally vertical platesorientated in a plane parallel to the feed direction 24. The guides 6can be moved transversely to the feed direction along transverse rods 30(only one of which is visible in FIG. 2) in order to adapt to paperstacks of various widths. Conventional means may be provided to releasethe guides 6 for sliding along the rods 30 and then to lock them againin the desired position. Although in FIG. 2 the two side guides 6 areboth displaced to their maximum extent in the same direction, in normaloperation the two guides 6 would be spaced equidistantly on either sideof the centreline of the sheet feeder, in order that the fed sheetsshould be centred on the drive unit 40 and be drawn through the devicewithout any off-centre forces. A scale 32 marked in suitable units withmeasurements of distance away from the centreline can be provided toassist the operator with positioning the guides 6. A known balancingmechanism (not shown) may also be provided to keep the guides positionedsymmetrically about the centreline.

Conventional side guides often have an L-shaped cross-section so thatthe edges of the bottom sheet of the stack rest on inwardly directedhorizontal portions of the guides. In the present apparatus it ispreferred that the side guides 6 should have no horizontal portions inorder that the bottom of the stack should make maximum contact with thefeed rollers 22. FIG. 6 shows schematically the relationship between thebottom of the side guides 6 and a set of the rollers 22. It does notattempt to show the mechanisms by which the guides 6 or rollers aremounted. The rollers 22 in the set define a plane 34 that is tangent tothe tops of the rollers, which is the plane in which the bottom sheet ofthe stack is supported. The lower edge of the side guide 6 comprises analternating series of cut-outs 36 and cusps 38. Each of the cut-outs 36is preferably in the form of a circular arc that is concentric with theaxis of an associated roller 22 to provide sufficient clearance aroundthat roller so that its rotation is not impeded. Each cusp 38 may cometo a sharp point or it may be blunt, provided that the tip of the cuspextends below the plane 34 between a pair of adjacent rollers.

Thus the set of cusps 38 are able to provide guidance for the stack downto the bottom sheet of paper, which rests in the plane 34. If the loweredge of the side guide 6 was straight, it would have to be positioned ata height above the plane 34 sufficient to clear the tops of the rollers,which would leave room for at least the bottom sheet in the stack todrift sideways, beneath the guide 6. The cut-outs are not necessarilyformed by cutting: any suitable process such as stamping or moulding maybe used. The shape of the lower edge of the side guide 6 need not matchthat shown in the drawings: the important feature is that above therollers 22 the guide should not interfere with their rotation and thatbetween adjacent pairs of rollers the guide should project below theplane 34.

Reverting to FIG. 2, there can also be seen one of a pair ofacceleration rollers 46, which are located one above the other anddownstream from the gate 26 of the sheet feeder. A sheet of paper havingbeen drawn through the gate 26 by the drive belts 42 is fed between thecounter-rotating acceleration rollers 46, which grip the sheet betweenthem and urge it away from the gate 26 at an increased speed.

The acceleration rollers 46 deliver the sheet of paper to the creasingdevice 20, where it is fed between a pair of counter-rotating shafts 48,one of which is visible in FIG. 2. Mounted on the shafts 48 are drums50, which have frictional surfaces to grip the sheet between them anddraw it through the creasing device at the same speed as it left theacceleration rollers 46. Also mounted on the shafts 48 are processingdrums 52, which may comprise respective male and female drums forcreasing, perforating or cutting the sheet between them in a knownmanner. The positions of the drums 50,52 along their respective shafts48 can be changed to adapt to the width of the sheets of paper and tothe desired positions of the creases, perforations or cuts. On exitingthe creasing device 20, the sheets are delivered to the top of theoutput bin 10 (FIG. 1), where they collect in an output stack.

The acceleration rollers 46 preferably run at a high speed relative tothe speed of the drive belts 42. For example, they may accelerate thesheets of paper to five times the speed at which they are driven by thedrive belts 42. Paper is delivered more-or-less continuously from thestack by the drive unit 40 so that the front edge of one sheet closelyfollows the rear edge of the preceding sheet through the gate 26. Theacceleration of the sheets by the acceleration rollers 46 causes a gapto open up between successive sheets, which may be useful in downstreamprocessing. For example, if instead of being collected in the output bin10, the output sheets are to be delivered one at a time to a secondmachine, it is sometimes the case that the second machine requires itsinput feed path to be arranged perpendicularly to the output feed pathof the present creasing machine. A gap between successive sheets allowstime for one sheet to change direction and clear the feed path beforethe next sheet arrives.

FIGS. 3, 4 and 5 show in more detail the removable drive unit 40 of thesheet feeder. The two drive belts 42 are spaced at equal distances fromthe centreline, on opposite sides of it. Each belt forms a continuousloop around first and second drums 68,70. The pair of first drums 68 ismounted on a common first shaft 69 beneath the feed deck 4, upstream ofthe gate 26. The pair of second drums 70 is mounted on a common secondshaft 71 at a corresponding level but slightly downstream of the gate.The second shaft 71 carries a gear 72, which is driven by a motor (notshown) to rotate both shafts 69,71 and drive the belts 42. The shafts69,71 are rotated in the anti-clockwise direction as viewed in FIG. 4,in order to drive the belts 42 along the feed deck 4 towards and throughthe gate 26. The belts 42 are made of rubber or a similar material thatmakes sufficient frictional contact with the overlying paper, such thatfrictional forces holding the bottom sheet against the next sheet in thestack are overcome and the sheet is carried by the belts 42 through thegate 26.

The drive unit 40 comprising the drive belts 42 is supported by a frame54. The frame 54 has a latch 56 at one end and a fixing screw 58 at theother end, whereby unfastening of the fixing screw 58 allows the entiredrive unit 40 to be quickly removed from the creasing machine 2, forexample so that worn drive belts 42 can be quickly replaced. The latch56 comprises a pair of fixed jaws 57 that can respectively engage withand pivot about a pair of rods 59 that form part of the substructure 60of the feed deck 4. Alternatively, the rods 59 could be located on theremovable drive unit 40 and the jaws 57 on the substructure 60. Thedrive unit can thus be removed from the feed deck 4 by unscrewing thesingle fixing screw 58, lifting the upstream end of the unit 40 to pivotthe jaws 57 of the unit about the rods 59 until the upstream end isclear of the deck 4, then withdrawing the unit 40 along its length,generally in the upstream direction, to free the jaws 57 from the rods59. The operation can be reversed to replace the drive unit 40. When thedrive unit is in its installed position, the first gear 72 comes intoengagement with a second gear (not shown) that is mounted beneath thefeed deck 4 and that provides rotary power to the drive unit 40 from themotor (not shown).

The delivery of sheets of paper from the stack is controlled by a pairof feed blocks 62 that are mounted by a bracket 64 on a frame of thesheet feeder so that each feed block 62 is suspended above a respectiveone of the drive belts 42. A friction pad 66 projects from the bottom ofeach feed block 62 towards the associated drive belt 42 to define thegate 26 therebetween, through which only one sheet at a time can pass.The size of the gate 26 (i.e. the vertical gap between the friction pad66 and the belt 42) can be manually adjusted by using knobs 68 to turn ato screw thread connection between each feed block 62 and the bracket64, thereby raising or lowering the feed block 62. The gate 26 is mosteasily set to the correct value for the thickness of paper to beprocessed by opening the gate, inserting a sheet of the paper betweenthe friction pad 66 and the drive belt 42 and then closing the gateuntil the sheet is almost trapped. This ensures that no more than onesheet of paper at a time can pass through the gate. The adjustment knobs68 are easily accessible during use of the machine so the size of thegate 26 can be fine-tuned during operation.

An alternative arrangement (not illustrated) is possible, in which thevertical position of the bracket 64 is adjustable relative to the frameof the machine, preferably by means an adjustment knob similar to thoseillustrated. It is preferred that at least one of the feed blocks 62should still be adjustable relative to the bracket in order thatindependent adjustment of the two feed blocks 62 remains possible, forexample in case the two drive belts 42 should wear down at differentrates.

A front face 70 of each feed block 62 faces upstream towards the feeddeck 4. When a stack of sheets 65 is placed on the feed deck 4, as shownschematically by dot-dash lines in FIG. 4, the stack slides on the feedrollers 22 down the inclined surface of the feed deck 4 until the frontedges of the sheets in the stack 65 come to rest against the front face70 of the feed block 62. The front face 70 at least partly forms anacute angle with the plane of the feed deck 4, which allows the lowersheets in the stack to travel further than the upper sheets and deformsat least the lower part of the stack 65 into a wedge. Successive sheetsin the stack are thereby slightly offset from one another along the feeddirection 24, which begins the process of separating them to passindividually through the gate 26. It is preferred that a first, lowerportion 72 of the front face 70 is inclined at an angle of less than 45°to the feed deck and preferably at between 25° and 30°. A second, upperportion 73 of the front face which merges smoothly into the lowerportion 72, need not be inclined at such a sharp angle. The anglebetween the upper portion 73 and the feed deck 4 may suitably beanywhere between 45° and 90° but a value between 60° and 70° ispreferred.

The shapes of the feed block 62 and the friction pad 66 are shown inmore detail in FIGS. 7 to 9, while their particular dimensions in theillustrated embodiment are marked on FIGS. 10 and 11.

It is believed that the geometry close to the gate is most important inproducing a reliable sheet feeder, i.e. one that can rapidly andconsistently transport one sheet at a time through the gate withoutjamming. The bottom of the feed block 62 is defined by a bottom face 74that is generally parallel to the surface of the drive belt 42. Thebottom face 74 is smoothly connected to the lower portion 72 of thefront face 70 by a curved transitional surface 76. As best seen in FIG.9, the lower part of each feed block 62 takes the form of two sidewalls78 with a recess 80 between them. The bottom face 74 of each feed block62 therefore in fact comprises a pair of discrete surfaces on therespective sidewalls 78. The friction pad 66 is mounted in the recess 80between the sidewalls 78 so that it projects slightly below the bottomface 74 of the feed block 62. The friction pad 66 is bounded by agenerally cylindrical surface 82, except that at the lowermost part ofthe projecting portion, the cylindrical surface 82 is replaced by a flatsurface 84 parallel to the drive belt 42. It is therefore the flatsurface 84 of the friction pad 66 that defines the gate 26. Theprojecting portion of the friction pad 66 also comprises on its upstreamside an exposed section 85 of the cylindrical surface 82 that isinclined at a sharp angle (less than 45°) to the drive belt 42. It isimportant to note that the friction pad 66 does not intersect the plane86 that is defined by the lower portion 72 of the front face 70 of thefeed block, as indicated by a dashed line in FIG. 7.

It is possible that the lower portion 72 of the front face of the feedblock 70 may be gently curved, rather than truly straight, and thereforenot define a true plane over its whole length. In that case, the plane86 in question, which is not intersected by the friction pad 66, is thattangent to the lowest part of the lower portion 72 before it transitionsinto the bottom face 74 via the curved surface 76.

The friction pad 66 is formed from a resilient material such as rubberor, preferably, polyurethane. Polyurethane has been found to work with aType A Shore hardness of 65, 80 or 90. Because the friction pad 66 isresilient rather than completely rigid, and because the geometry of thegate is important, means need to be provided to mount the pad 66securely in the recess 80. The pad 66 is fixed at two points to preventit pivoting. At each fixing point a horizontal bore passes through thepad 66 and is lined with a metal (e.g. steel) bush 88 that is internallythreaded. Four bolts 90 are then passed through apertures in theopposing side walls 78 of the feed block 62 and are screwed into theeach end of each bush 88 to secure the friction pad 66 against movement.

The feed blocks 62 may be manufactured from any suitable, rigidmaterial, for example aluminium or an aluminium alloy. It is preferredthat the surfaces of the feed blocks 62 and in particular the frontsurfaces 70 that contact the stack of paper should be anodized toprovide them with a smooth and durable finish.

1. A sheet feeder comprising: a feed deck for supporting a stack ofsheets to be fed; a feed block; a drive belt for frictionally engagingthe underside of a bottom sheet of the stack and urging the sheet belowthe feed block along a feed direction; wherein the feed block comprises:a friction pad that projects from the bottom of the feed block towardsthe drive belt to define a gate therebetween; and a first front faceimmediately upstream from the gate, the first front face defining aplane inclined at a first angle to the feed direction; wherein thefriction pad does not intersect the plane of the first front face. 2.The sheet feeder according to claim 1, wherein the first angle is lessthan 45°.
 3. The sheet feeder according to claim 2, wherein the firstangle is between 25° and 30°.
 4. The sheet feeder according to claim 1,wherein the feed block further comprises a second front face upstreamfrom the first front face, the second front face being inclined to thefeed direction at a second angle that is greater than the first angle.5. The sheet feeder according to claim 1, wherein the feed block furthercomprises a lower face, which is located downstream from the first frontface and which faces the drive belt, the friction pad projecting fromthe bottom of the feed block below the lower face.
 6. the sheet feederaccording claim 5, wherein lower face of the feed block defines a planethat is substantially parallel to the feed direction; the feed blockfurther comprising a curved surface that effects a smooth transitionfrom the first front face to the lower face.
 7. The sheet feederaccording to claim 1, wherein the friction pad comprises a pad lowerface that is substantially parallel to the feed direction.
 8. The sheetfeeder according to claim 7, wherein the friction pad further comprisesa pad front face that adjoins an upstream end of the pad lower face, thepad front face being inclined at an angle of less than 45° to the feeddirection where it adjoins the pad lower face.
 9. The sheet feederaccording to claim 8, wherein the pad front face is part of asubstantially cylindrical surface that surrounds the friction pad exceptin the region of the pad lower face.
 10. The sheet feeder according toclaim 1, wherein the material of the friction pad is polyurethane. 11.The feeder according to claim 1, wherein the material of the frictionpad has a Type A Shore hardness in the range 50 to
 100. 12. the sheetfeeder according to claim 11, wherein the material of the friction padhas a Type A Shore hardness in the range 85 to
 95. 13. The sheet feederaccording to claim 1, wherein the feed block comprises a pair ofsidewalls and a recess in the bottom of the feed block extending betweenthe sidewalls, the friction pad being mounted in the recess.
 14. Thesheet feeder according to claim 13, wherein the friction pad comprisesat least two bores therein, the friction pad being mounted in the recessby at least two fixings that pass through the sidewalls of the feedblock and engage with the bores.
 15. The sheet feeder according to claim1, wherein the material of the feed block is aluminium or an aluminiumalloy; and wherein at least the first front face of the feed block isanodized.
 16. The sheet feeder according to claim 1 comprising a pair ofthe drive belts positioned on opposite sides of a centreline of the andpair of the feed block aligned with respective ones of the drive belts.17. The sheet feeder according to claim 16, wherein the pair of feedblocks are mounted on a common bracket, which is in turn mounted on aframe of the sheet feeder.
 18. The sheet feeder according to claim 17,further comprising means for adjusting the height of at least one of thefeed blocks relative to the bracket.
 19. The sheet feeder according toclaim 17, further comprising means for adjusting the height of thebracket relative to the frame.
 20. The sheet feeder according to claim1, further comprising a counter-rotating pair of acceleration rollersdownstream from the gate for gripping a sheet between them andaccelerating the sheet away from the gate.
 21. The sheet feederaccording to claim 1, wherein the feed deck is inclined to thehorizontal and wherein the feed deck comprises a plurality of feedrollers, each of which is free to spin about a generally horizontalaxis.
 22. The sheet feeder according to claim 21, further comprising atleast one guide plate arranged in a vertical plane and transversely to aset of the rollers, the set of rollers defining a plane that is tangentto the tops of the rollers wherein a lower edge of the guide plateprojects below the between adjacent pairs of the rollers.